Oddly enough, he also has posted the following tidbits on the Internet: his employer, the type of gun he owns, his photograph — and the fact that he and his girlfriend "have sex marathons from sundown til sunrise." Snowden used a pseudonym, but it was transparent, given the personal information he disclosed.

In our culture, both digital exhibitionism and digital don't-tread-on-me-ism are on the rise. Privacy law may be about to get more complex than it already is.

The Supreme Court defines Fourth Amendment protections in terms of a "reasonable expectation of privacy."

If you do, say, write or possess something in circumstances suggesting that you expect it to be private, and if society in general would share your expectation, then it's protected. Government can't intrude without a warrant.

It's far from a perfect rule. As Jay Stanley of the American Civil Liberties Union aptly notes, "It bases law and practice on the subject's understanding of law and practice." But the rule kinda, sorta works — assuming courts update "reasonable expectations" in keeping with cultural and technological change.

Alas, cultural and technological change are moving too fast for the doctrine. Consensus about propriety — about what "ladies" and "gentlemen" do and don't discuss in public — is long gone. And because of technology, "public" is practically everywhere, all the time.

The Supreme Court wrestled with this problem in U.S. vs. Jones, decided a year before Snowden's emergence. Police stuck a GPS tracking device to the undercarriage of a drug suspect's car to help build a case against him. All nine justices agreed that the police should have gotten a warrant, but only because attaching the GPS tracker amounted to a "physical intrusion" of the car.

On the big question — whether sustained technological surveillance, conducted without physical intrusion, would have violated today's reasonable expectations of privacy — the court produced no majority opinion.

In a concurring opinion, Justice Sonia Sotomayor anticipated Snowden, voicing alarm that individuals' movements might be "recorded and aggregated in a manner that enables the government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on."

So what if you traveled where the government could have tracked you by conventional means? For Sotomayor, that doesn't create a "reasonable expectation" of data-mining. She would revisit the "reasonable expectations" doctrine, especially the part that supposes you have no privacy interest in information — like your car's path on public roads or telephone "metadata" — disclosed to third parties.

Yes, there's a difference between things we voluntarily publicize — like Snowden's pseudonymous musings about sex — and the digital bread crumbs we involuntarily leave for government and corporations to gather.

Still, Sotomayor seemed to take that point a bit too far. Quoting a lower court judge, Sotomayor alluded to "indisputably private … trips to the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, the gay bar and on and on." While all of these examples are potentially controversial, none is "indisputably" private by today's standards; church strikes me as usually pretty public, actually.

In another concurring opinion, Justice Samuel A. Alito Jr. doubted the constitutionality of lengthy warrantless GPS surveillance but noted realistically, "New technology may provide increased convenience or security at the expense of privacy, and many people may find the trade-off worthwhile. And even if the public does not welcome the diminution of privacy that new technology entails, they may eventually reconcile themselves to this development as inevitable."

Alito suggested that legislatures, not courts, should take the lead in defining privacy law, since they are better "situated to gauge changing public attitudes, to draw detailed lines, and to balance privacy and public safety in a comprehensive way."

Still, the only thing less workable than the "reasonable expectations" doctrine might be constant political attempts to account for what every individual might feel like broadcasting, or accept as "inevitable."

In 1929, Secretary of State Henry L. Stimson closed the State Department office that intercepted and decoded foreign diplomatic letters, explaining that "gentlemen do not read other gentlemen's mail."

We need rules for a generation that reads Stimson's words and wonders: What's a gentleman? And what's mail?